This invention relates to a working apparatus for doing works in a lower part of the inside of a nuclear reactor or the like and a working method of operating such an apparatus.
Intra-nuclear-reactor working apparatus are generally used for intra-reactor operations such as inspections, examinations and preventive maintenances of the inner surface of nuclear reactor pressure vessels (RPVs) and intra-reactor structures. Particularly, when the weld line found in a lower part of the shroud support plate of a lower part of a boiling water nuclear reactor is the target of operation, it is difficult for the intra-nuclear-reactor working apparatus to get to the weld line and the operation faces various problems such as a limited working space and a long working time because it is difficult to access the target that is located in a very narrow area. Various intra-nuclear-reactor working apparatus have been proposed to carry out such an operation in a short period of time and secure a larger working space at a place having access difficulties.
Firstly, an intra-nuclear-reactor working apparatus comprising a remotely operated vehicle (ROV) to be used in water that is equipped with a thruster for moving back and forth and for turning, a thruster for moving up and down and for moving sideways and an underwater camera is known (See, inter alia, Japanese Patent Application Laid-Open Publication No. Hei 11-14784, the entire contents of which being incorporated herein by reference). The apparatus disclosed in the cited reference is provided with an arm mechanism that can be turned and an inspection means selected from an ultrasonic inspection means, a radiation-resistance television camera, an infrared camera and so on is replaceably fitted to the front end of the mechanism.
In this known apparatus, an X-Y scanner mechanism is arranged at the front end of the arm mechanism and any of a various inspection means is fitted to the scanner mechanism. For example, the arm mechanism and the selected inspection means are conveyed to the site of inspection by means of the thrusters of the underwater ROV and the X-Y scanner is pressed near the target of inspection and operated to scan the target by the selected inspection means, utilizing the degree of freedom of operation of the X-Y scanner.
Secondly, a vehicle type mobile body designed to be used as intra-nuclear-reactor working apparatus as described below is known (See Japanese Patent Application Laid-Open Publication No. 2001-296385, the entire contents of which being incorporated herein by reference). This apparatus has a plurality of wheeled arms (cylinder rods) to be extended under the shroud support plate toward the RPV and the shroud support to make the apparatus itself to be preliminarily anchored there. Then, thrusters or the wheels that the mobile body is provided with are driven to move the apparatus to the working site along the periphery. The pressure being applied to the cylinder rods is raised there in order to securely anchor the apparatus.
The apparatus is held in position by the wheels that are pressed by unfolding the work reaction force exerted by the object of work, in other words, the apparatus can hold a large work reaction force. Additionally, it is possible to accurately position the apparatus in a peripheral direction so that the apparatus can be highly reliable in repeated positioning by driving the wheels to travel and move.
VT (visual testing) apparatus realized by mounting an inspection camera on a swimming type vehicle and UT (ultrasonic testing) apparatus realized by combining a swimming type vehicle and an arm to mount a UT probe for the purpose of inspecting weld lines in water located under the shroud support plate in a lower part of the core are known.
It is possible to inspect a broad area in a short period of time in order to efficiently perform an assigned work by using such a swimming type vehicle and auxiliary mechanisms such as arms, because of their mobility and flexibility.
However, preventive maintenance works and welding works involving brush polishing, water washing, water jet peening and/or laser peening encounter a large reaction force in the work, and hence it is difficult to carry out the work by using a swimming type vehicle for conveying objects, positioning itself and holding the position. Additionally, it is difficult for such a swimming type vehicle to move accurately and position itself to give rise to a difficulty in repeated positioning.
On the other hand, a system for unfolding traveling wheels toward the inner wall of a pressure vessel and a shroud support, anchoring itself to a given position and driving thrusters or wheels to move horizontally, can utilize a large reaction force in the work to support itself and move and position itself accurately.
However, when such a system is driven to travel by means of wheels in a peripheral direction of the shroud or the RPV, it can be vertically displaced. It is difficult to prevent or suppress such a vertical displacement.
In view of the above-identified problems of the prior art, it is therefore an object of the present invention to provide a working apparatus and a working method that are adapted to move over a broad range within a short period of time with a limited number of setting operations, withstand a large reaction force and easily position itself repeatedly, moving along a structure in water and positioning itself.